Clay mineral composition of shelf sediments off the east coast of India

The clay mineral composition of the sediments carpeting the continental shelf off the east coast of India has been determined by X-ray and Differential Thermal Analysis techniques. Sediments contributed by the Ganges-Brahmaputra system of rivers are composed of about equal quantities of chlorite and illite with a small amount of montmorillonite and a trace of kaolinite. On the other hand, sediments from near the confluence of the Godavari river are composed of a mixture of very poorly ordered clay minerals; and those derived from the Krishna river comprise illite, montmorillonite, and mixed-layers of these minerals. Sediments off Visakhapatnam, which are accumulating at a place relatively free from the influence of the terrigenous influx from the major rivers, are composed of illite, montmorillonite, mixed-layer montmorillonite and illite, with a trace of chlorite, and kaolinite. The contrasted clay mineral assemblages have been attributed primarily to the difference in the source rocks and their weathered products in the respective drainage basins of these rivers rather than to diagenesis in the marine environment.